1. Field of the Invention
The present invention relates to the technical field of liquid crystal display driving circuit, and particularly to a designing method and circuit of gray level and luminance characteristic of liquid crystal display.
2. Description of the Related Art
In designing the driving circuit chip of a liquid crystal display (LCD), since it is necessary to provide different gray level voltages to the liquid crystal display, the driving circuit chip needs a plurality of reference voltages to generate gray level voltages for the liquid crystal display. For example, with reference to FIG. 1, for a liquid crystal display of 64 levels, the driving circuit chip 11 needs 10 sets of reference voltages V0˜V9 supplied by the power supply circuit 12 for matching 6 bit display data to generate the outputs of 64 high voltage gray levels and 64 lower voltage gray levels. FIG. 2 shows the relation of the input 6 bit display data and the output voltage. The voltages V0˜V4 larger than the common voltage VCOM are high voltages, and the voltages V5˜V9 smaller than the common voltage VCOM are low voltages. V5 is a white signal low voltage and V9 is a black signal low voltage.
In designing the driving circuit chip, the electric characteristic can be determined according to the specification of the chip. However, this only assures the system to operate normally, while the overall gray level and luminance characteristic of the liquid crystal display can not be estimated. Only after the liquid crystal display is actually completed, it is able to perform the optimal adjustment of the gray level and luminance characteristic based on the reference voltage, which results in increasing the cost and time required for adjustment and design. Moreover, each reference voltage occupies one wire layout on the circuit board. The increment of the reference voltages will increase the number of wires so that the area of the circuit board will be too large, and thus the product can not be made as small as required. Thereby, aforesaid driving circuit chip of a liquid crystal display is not ideal and is necessary to be improved.